TI99Sim is a very good emulator of Texas Instruments
TI99 home computer running on Windows and Unix.
The emulator faithfully imitates the TI99/4 model
(see http://www.mrousseau.org/programs/ti99sim/)
GP2X-TI99 is a port on GP2X of the version 0.1.0 of TI99Sim.
How to use it ? Everything is in the README.txt file.